setup: kill remaining nose whims to be around

requirements-test.txt

@@ -1,3 +1,3 @@
-nose
+pytest
 requests_mock
 testing.postgresql

setup.py

@@ -47,7 +47,6 @@ setup(
     scripts=['bin/ghlister'],
     install_requires=parse_requirements() + parse_requirements('swh'),
     tests_require=parse_requirements('test'),
-    test_suite='nose.collector',
     setup_requires=['vcversioner'],
     extras_require={'testing': parse_requirements('test')},
     vcversioner={'version_module_paths': ['swh/lister/_version.py']},